mk-ca-bundle.vbs: Fix UTF-8 output

- Change initial message box to mention delay when downloading/parsing.

Since there is no progress meter it was somewhat unexpected that after
choosing a filename nothing appears to happen, when actually the cert
data is in the process of being downloaded and parsed.

- Warn if OpenSSL is not present.

- Use a UTF-8 stream to make the ca-bundle data.

- Save the UTF-8 ca-bundle stream as binary so that no BOM is added.

---

This is a follow-up to d2c6d15 which switched mk-ca-bundle.vbs output to
ANSI due to corrupt UTF-8 output, now fixed.

This change completes making the default certificate bundle output of
mk-ca-bundle.vbs as close as possible to that of mk-ca-bundle.pl, which
should make it easier to review any difference between their output.

Ref: https://github.com/curl/curl/pull/1012

lib/mk-ca-bundle.pl

@@ -30,6 +30,7 @@
 # dependency is the OpenSSL commandline tool for optional text listing.
 # Hacked by Guenter Knauf.
 #
+use Encode;
 use Getopt::Std;
 use MIME::Base64;
 use strict;
@@ -487,7 +488,7 @@ while (<TXT>) {
               . "-----END CERTIFICATE-----\n";
       print CRT "\n$caname\n";
       print CRT @precert if($opt_m);
-      my $maxStringLength = length($caname);
+      my $maxStringLength = length(decode('UTF-8', $caname, Encode::FB_CROAK));
       if ($opt_t) {
         foreach my $key (keys %trust_purposes_by_level) {
            my $string = $key . ": " . join(", ", @{$trust_purposes_by_level{$key}});